1. Field of the Invention
The present invention relates to an automobile trim in which a decorating layer is formed of a TPE (thermoplastic elastomer) composition and integrated with a design surface of a trim body which is formed of a rubber composition.
Here, a weather strip (automobile trim) having a trim portion and a seal portion will be mainly described as a product to which the present invention is applied, by way of example. The present invention is applicable also to a weather strip of another type, such as a glass run having a trim portion, or the like. Further, the present invention is applicable also to an automobile trim having only a trim portion without having any seal portion.
The present application is based on Japanese Patent Applications Nos. 2000-60000 and 2000-278062, which are incorporated herein by reference.
2. Description of the Related Art
A trim portion and a seal portion of a weather strip are usually manufactured using EPDM (ethylene-propylene-diene copolymer) compositions of a solid recipe and a foam recipe, respectively, by two-layer extrusion (co-extrusion) by using a two-layer extruder. The reason why such EPDM compositions are used is that they are superior in weatherability and elasticity and low in specific gravity so that they can contribute also to making the weather strip light in weight. A sulfuric vulcanizer which is a general-purpose vulcanizer is usually used for vulcanizing the EPDM compositions. That is because hot-air vulcanization used for continuous vulcanizing extruded products is applicable to the sulfuric vulcanizer differently from other general-purpose vulcanizers of peroxides.
Then, for forming the decorating layer in the trim portion, there are methods in which a decorating layer composed of TPE (composition), which has not solidified yet, is laminated and integrated on the surface of a trim body (base layer) by thermal bonding without using any bonding agent (U.S. Pat. No. 4,537,825, European Patent No. 0372745, and Unexamined Japanese Patent Publication No. Hei. 8-230013). These methods are more superior in productivity to conventional methods in which a soft thermoplastic resin sheet is cut out and bonded by a bonding agent so as to form a decorating layer. Here, the reason why the decorating layer is formed of TPE is to ensure the easiness of bending when the trim portion of the weather strip is attached to a vehicle body flange or the like.
However, in the weather strip configured so that the decorating layer formed by the above-mentioned method has been thermally bonded integrally with the surface of the trim body, it has been found that the following problems occur in the decorating layer.
(1) The decorating layer is affected by the ground color of the trim body (base layer) so that the decorating layer is difficult to exhibit a required color. This is because a large quantity of carbon black as a rubber reinforcement is mixed into the solid-recipe EPDM composition for forming the trim body so that the solid-recipe EPDM composition has a high degree of blackness (chroma saturation).
(2) The decorating layer is affected by sunlight chronologically so that the decorating layer is apt to yellow. As the cause thereof, it has been confirmed that there is a high possibility that such yellowing is caused by the migration of a sulfuric vulcanizing agent (sulfur and vulcanizing accelerator thereof) in vulcanized rubber to the decorating layer (see Unexamined Japanese Patent Publication No. Hei. 9-193299).
The influence of the ground color and the yellowing degree in the decorating layer becomes more conspicuous if the coloring of the decorating layer is bright or pale. That is, in the above-mentioned weather strip (trim) configured so that the decorating layer has been thermally bonded with the trim body, it is difficult to meet a request of making the decorating layer bright or pale.
To prevent the decorating layer from yellowing easily, it has been proposed in the above-mentioned patent publication (Unexamined Japanese Paten No. Hei. 9-193299) that hydrotalcite as an anti-discoloring agent is mixed into the TPE composition for forming the decorating layer.
However, hydrotalcite is currently so expensive as to increase the total material cost of the weather strip. Therefore, other measures against the yellowing of the decorating layer without using hydrotalcite are desired.
Further, a technique disclosed in Unexamined Japanese Patent Publication No. Hei. 6-16094 has also been known as such another automobile weather strip. This weather strip has a rubber base, a decorating skin material, and a cushion layer. The rubber base is composed of solid rubber of EPDM (aforementioned solid recipe) which is a kind of EPR (ethylene-propylene rubber). The decorating skin material (aforementioned decorating layer) covers a portion of the rubber base in the area where the rubber base (layer) is exposed in the cabin of a vehicle. The cushion layer is formed of sponge rubber of EPDM (aforementioned foam recipe) between the decorating skin material and the base (layer). The cushion layer sinks following external force through the decorating skin material, and restores its original shape in response to the release of the external force. Thus, the cushion layer provides a soft feeling on the sense of touch.
However, the decorating skin material attached to the surface of the cushion layer is of cloth using precolored polyester fibers as raw material, or of a resin sheet material such as PVC. Therefore, a soft feeling on the external appearance cannot be obtained from the skin material itself. In addition, in either case of polyester or PVC, they have no adhesive property to the rubber base of EPDM. Accordingly, it is necessary to prepare a special bonding film having a two-layer structure with adhesive properties to bond to the skin material and the EPDM rubber base respectively. As a result, the manufacturing cost is increased. Further, in this weather strip, the cushion layer is provided only between the apex portion of the sectionally U-shaped rubber base and the skin material. An outside lip projecting on the car-interior side is formed of solid rubber alone. Therefore, a soft feeling cannot be obtained in this portion sufficiently. Thus, there has been a problem that a soft feeling and a sense of high quality cannot be obtained sufficiently as a car interior material.